The present disclosure relates to a developing device for developing an electrostatic latent image on an image-carrier, and to an image forming apparatus including the developing device.
An image forming apparatus, such as a copier or a printer, that forms an image on a paper sheet based on the electrophotography is provided with a developing device. The developing device uses toner to develop an electrostatic latent image formed on an image-carrier such as a photoconductor drum. The developing device includes a developing roller that is positioned a certain gap apart from the image carrier. As the developing method, there is known a method that magnetically draws up developer including toner from the developer storing chamber onto the surface of the developing roller, and causes the toner to fly from the developing roller to be adhered to an electrostatic latent image on the image carrier by an electric field generated by a developing bias applied to the developing roller.
The developing device of this type includes a stirring member for conveying the developer to a position facing the developing roller while stirring the developer stored in the developer storing chamber. As the stirring member, there are known, for example: a screw rotation member with a blade member of a helical shape attached to a rotation shaft; and a paddle rotation member with a blade member of a paddle shape attached to a rotation shaft. When adopting either of these types of stirring members, a difference in thickness is made between developer on blades of the blade member facing the developing roller and developer on regions except for the blades. Due to this difference, a difference may be made in amount of developer drawn up to the developing roller. For example, when the blades of the blade member face the developing roller, a more amount of developer is drawn up than when the regions except for the blades face the developing roller. Such a difference in draw-up amount of the developer may cause a density variation with a striped pattern corresponding to the pitch of the blade member to appear on the image. As conventional apparatuses for reducing the density variation, there are known, for example: an apparatus that presses the developer against the surface of the developing roller by using a pressing member provided more on the downstream side in the rotation direction of the developing roller than the developer draw-up position; and an apparatus that improves the draw-up characteristic of drawing up the developer onto the developing roller by intervening an auxiliary member made of a magnetic material.